The present invention relates to a throttle valve opening sensor for use with an internal combustion engine.
Conventionally, a throttle valve opening sensor includes a housing, a substrate received in a substrate receiving hole formed in the housing, and a rotor adapted to rotate relative to the substrate in the housing. The substrate is fixed by a cover through a packing to the housing. The substrate is provided with a printed pattern of a throttle valve opening detecting portion consisting of a resistor and a collector both being in the configuration of partial sector and an idle position detecting portion consisting of a conductor and a collector. On the other hand, the rotor is provided with a first contact adapted to slide on the resistor and the collector of the opening detecting portion and with a second contact adapted to slide on the conductor and the collector of the idle position detecting portion.
In the conventional throttle valve opening sensor as mentioned above, the rotor is provided with a columnar projection at the central position thereof which projection is inserted into a central hole formed at the substrate, so as to make the center of the printed pattern on the substrate coincident with the center of the rotation of the rotor. However, it is necessary to make the diameter of the central hole of the rotor larger than the diameter of the columnar projection, so as to insert the projection into the central hole. As a result, the center of rotation of the rotor tends to become eccentric from the center of the hole of the substrate, losing the linearity between a rotative angle of the throttle valve and an output voltage. Furthermore, if the rotor is installed under the condition where the columnar projection is in contact with a part of the hole of the substrate, the rotor cannot be smoothly rotated. In the worst case, the columnar projection or the substrate is worn to generate a powder, and the powder is deposited on a sliding surface of the substrate on which the first and second contacts of the rotor are slided, thereby causing generation of electrical noise and adversely affecting accuracy of detection of the throttle valve opening sensor. The aforementioned prior art device is disclosed in Japenese Laid-Open Utility Model Publication No. 57-73332 and 59-41708.